1. Technical Field
The present invention relates to a shock absorber including a damping-force generating device that controls a flow of working fluid caused by sliding of a piston in a cylinder and thereby generates a damping force.
2. Related Art
As a shock absorber used as a rear cushion that suspends a rear wheel of a motorcycle on a vehicle body, for example, there is a shock absorber including a cylinder in which working fluid is sealed, a piston fitted in the cylinder to be capable of sliding, and a piston rod coupled to the piston and extended to an outside of the cylinder. The shock absorber includes a damping-force generating device that controls a flow of oil caused by the sliding of the piston in the cylinder and thereby generates a damping force.
In such a shock absorber, as a control valve for adjusting the damping force, for example, there is known a control valve including a valve body urged in a valve opening direction by urging means such as a spring, a valve seat on which the valve body is seated, and an actuator that moves the valve body in a valve closing direction by the thrust of a solenoid and seats the valve body on the valve seat.
The shock absorber including the control valve controls an electric current supplied to the solenoid, which is the actuator, to adjust, with the thrust of the solenoid, a load in the valve closing direction in which the valve body is seated on the valve seat, and thus controls an opening degree of the valve body to adjust a hydraulic pressure to thereby adjust the damping force.
In the shock absorber, at a failure time when the solenoid is broken down by some cause, energization to the solenoid is interrupted, and the solenoid does not generate the thrust, the valve body of the control valve moves with an urging force of the urging means and changes to a full-open state. Therefore, for example, the adjusted hydraulic pressure drops, the damping force suddenly decreases, and operation stability of a vehicle is hindered.
Therefore, Patent literature 1 (JP-A-2011-075060) proposes a shock absorber shown in FIGS. 23A and 23B. Note that FIGS. 23A and 23B are main part sectional views of the shock absorber proposed in Patent Literature 1. FIG. 23A shows a state at a normal time. FIG. 23B shows a state at the failure time.
In the shock absorber proposed in Patent Literature 1, a valve body 170 configuring a control valve for controlling a back pressure of a main valve, which controls a flow of oil caused by sliding of a piston in a cylinder to generate a damping force, is urged to a valve opening side (the right in FIGS. 23A and 23B) by a valve spring 173, which is urging means. An annular sheet disk 190 is fixed in contact with a rear end face (a right end face in FIGS. 23A and 23B) of the valve body 170. An annular sheet-like fail-safe valve 175 is disposed on a downstream side of the valve body 170. An outer circumferential portion of the fail-safe valve 175 is clamped and fixed by a pilot valve member 148 and a holding member 149.
The valve body 170 is attached to a distal end of an actuation rod 167 that moves in an axial direction (the left-right direction in FIGS. 23A and 23B) with thrust generated by a not-shown solenoid, which is an actuator. At the normal time when the solenoid normally operates, the valve body 170 moves with the thrust of the solenoid and is spaced from or seated on a circumferential edge of a port 171 of a pilot valve member 148 as shown in FIG. 23A to thereby open and close the port 171. Note that, at the normal time, the valve body 170 and the sheet disk 190 in contact with the valve body 170 are spaced from the fail-safe valve 175. Therefore, a pilot channel 150 is always in an open state.
At the normal time when the solenoid normally operates, it is possible to control a supply current to the solenoid and adjust a valve opening pressure of the valve body 170 to thereby adjust an internal pressure of a not-shown pilot chamber (the back pressure of the not-shown main valve) and thereby control the opening degree of the main valve to adjust the damping force.
At the failure time when the solenoid does not normally operate because of, for example, disconnection of a coil, the solenoid does not generate the thrust. Therefore, the valve body 170 and the sheet disk 190 in contact with the valve body 170 move in a valve opening direction (the right in FIGS. 23A and 23B) with the urging force of the valve spring 173 as shown in FIG. 23B. An outer circumferential portion of the sheet disk 190 comes into contact with an inner circumferential portion of the fail-safe valve 175 and closes the pilot channel. When the internal pressure of the pilot chamber reaches a predetermined value in this state, the fail-safe valve 175 bends centering on the outer circumferential portion as indicated by a dotted line in FIG. 23B and flows fluid. Therefore, a sudden decrease in the internal pressure of the pilot chamber is prevented by the flow resistance of the fluid. Consequently, a sudden decrease in the damping force due to a sudden increase in the opening degree of the main valve is prevented.